Sampling frequency down-converting apparatus

Abstract

A sampling frequency down-converting apparatus low-pass converts a digital picture signal sampled at a sampling frequency of 8 Fsc by a thinning out operation into the digital picture signal sampled at a frequency of 4 Fsc, and a sampling frequency up-converting apparatus high-pass converts the digital picture signal sampled at 4 Fsc into one sampled at 8 Fsc by interpolation. If the signal is wider in the required zone than the conventional NTSC signal and the PAL signal like the ATV signal, the transmission and the recording may be effected without the deterioration of the frequency characteristics.

What is claimed is: 
     
       1. A sampling frequency down-converting apparatus comprising a means for sampling original digital picture signals at a sampling frequency of 8 Fsc (Fsc: color sub-carrier frequency) so as to thin out said sampled picture signals and a means for low-pass converting said sampled picture signals into intermediate digital picture signals having a sampling frequency of 4 Fsc ±Fh/2 (Fh: horizontal scanning frequency) or 4 Fsc ±Fv/2 (Fv: field frequency). 
     
     
       2. A sampling frequency down-converting apparatus comprising: a first delay means for delaying by 262H an original digital picture signal having a sampling frequency of 8 Fsc (Fsc: color sub-carrier frequency); a first filter for zone restricting the delay output of the first delay means; a second filter for zone restricting the original digital picture signal; a first adder for adding the output of the first filter and the output of the second filter; a second delay means for delaying the delay output of the first delay means by n samples (n is a positive integer; a second adder for adding the output of the first adder and the output of the second delay means; a means for thinning out a processed original digital picture signal having a sampling frequency of 8 Fsc which is the output of the second adder into an intermediate digital picture signal, which has a sampling frequency of approximately 4 Fsc. 
     
     
       3. A sampling frequency down-converting apparatus described in accordance with the claim 2, wherein the central frequency of the frequency characteristics of the second filter is made twice the color sub-carrier frequency. 
     
     
       4. A sampling frequency down-converting apparatus described in accordance with the claim 3, wherein the characteristics of the second filter becomes 0 in amplitude at the color sub-carrier frequency. 
     
     
       5. A sampling frequency down-converting apparatus described in accordance with the claim 3, wherein the coefficient multiplier constituting the second filter has coefficients which are made the seventh of -1, 4, -7, 8, -7, 4, -1, in the order of the flow of the original digital picture signal. 
     
     
       6. A sampling frequency down-converting apparatus described in accordance with the claim 3, wherein the coefficient multiplier constituting the second filter are made the seventh of -5, 16, -27, 32, -27, 16, -5 in the order of the flow of the signals. 
     
     
       7. A sampling frequency down-converting apparatus comprising a means for sampling original digital picture signals at a sampling frequency of N Fsc (Fsc: color sub-carrier frequency and N is an integer =16, 8) so as to thin out said sampled picture signals and a means for low-pass converting said sampled picture signals into intermediate digital picture signals when have a sampling frequency of N/2 Fsc ±Fv/2 (Fh: horizontal scanning frequency) or N/2 Fsc ±Fv/2 (Fv: field frequency). 
     
     
       8. A sampling frequency down-converting apparatus comprising a first delay means for delaying by 262H an original digital picture signal having a sampling frequency of N Fsc (Fsc: color sub-carrier frequency and N is an integer =16, 8); a first filter for zone restricting the delay output of the first delay means; a second filter for zone restricting the original digital picture signal; a first adder for adding the output of the first filter and the output of the second filter; a second delay means for delaying the delay output of the first delay means by n samples (n is a positive integer; a second adder for adding the output of the first adder and the output of the second delay means; a means for thinning out a processed original digital picture signal having a sampling frequency of N/2 Fsc which is the output of the second adder into an intermediate digital picture signal, which has a sampling frequency of approximately N/4 Fsc. 
     
     
       9. A sampling frequency down-converting apparatus descried in accordance with claim 8, wherein the central frequency of the frequency characteristics of the second filter is made twice the color sub-carrier frequency. 
     
     
       10. A sampling frequency down-converting apparatus described in accordance with claim 9, wherein the characteristics of the second filter becomes o in amplitude at the color sub-carrier frequency.